Device manufacturers may have hit the sweet spot in tablet designs and form factors. While Apple had initially eschewed the 7-inch form factor as being too small to be of any use, it seems 7-inch tablets are now the best-selling product lines in both Android and iOS ecosystems.

In fact, sales of 7-inch tablets have been hurting the growth of the full-sized iPad, which had traditionally led the pack in tablet sales. As of fourth quarter of 2012, the year-over-year growth of iPad sales has dwindled to 1.8 percent, and even fell 9 and 26 percent in the U.S. and Japan, respectively.

During this period, 7-inch tablets took 41.2 percent market share, up from 12.6 percent in 3Q 2012. Meanwhile, 10-inchers fell in market share from 67.3 percent to 40.6 percent.

This is from analysis shared by Glen Yeung, Apple analyst at Citi Research, and based on data released by IDC. “Beyond simply the overall share loss, the data reveals a particular slowdown in 10-inch iPad sales in mature markets,” Yeung said. “After analyzing the data, we have new concerns about the health of the 10-inch tablet market and, absent any material innovations (we do not count a Retina Mini or lighter/thinner iPad 5 among these), we remain concerned about Apple’s ability to maintain market share.”

This might be a result of several factors. First, the more mature markets, such as Japan and the U.S., are likely to be already saturated in terms of full-size tablets. Secondly, unlike smartphones, which can be renewed under carrier contract every couple of years, tablets are considered a longer-term investment.

There is also the price factor. Seven inchers like the Google Nexus 7 start for US$299. Even Apple’s own iPad Mini starts at US$329 for the most basic model. With lesser-known brands also selling Jelly Bean tablets for less than the US$150 price factor, then these are surely more attractive than the US$499 starting price for the 9.7-inch iPad and similarly-priced Android offerings.

In fact, the 7-inch form factor is also growing in popularity among manufacturers. DigiTimes reports that 7-inch display panels will drive growth for display manufacturer starting this year.

Forbes actually predicted the rise of the 7-inch tablet back in 2010, but the iPad Mini and Google Nexus 7 have yet to materialize during that time. Now it seems the market is ready for (relatively) inexpensive 7-inch tablets, and recent traffic statistics also support this trend.